16/9/2011ucerf3 / eq simulators workshop rsqsim jim dieterich keith richards-dinger uc riverside...
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1 6/9/2011 UCERF3 / EQ Simulators Workshop
RSQSim
Jim DieterichKeith Richards-Dinger
UC Riverside
Funding: USGS NEHRPSCEC
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Representation of Fault Friction• Constitutive relation:
• State evolution:
• Stress evolution:
• Terms in red are additional ones due to normal stress variations (Linker and Dieterich, 1992)
• Interaction coefficients, K, calculated from the dislocation solutions of Okada, 1992
• Tectonic stressing rates derived from backslipping the model
• Numerical integration too slow for the scale of problems we would like to address
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Representation of Fault Friction• Constitutive relation:
• State evolution:
• Stress evolution:
State 1: nucleation State 0: locked fault
State 2: seismic slip
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Representation of Fault Friction• No predetermined failure stress or stress drop• Stress drop scales roughly as
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Representation of Fault Friction• No predetermined failure stress or stress drop• Stress drop scales roughly as
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Approximations to Elastodynamics
Parameters that influence the rupture process:• Slip speed during coseismic slip determined from
shear impedance considerations• Reduction of a on patches nearby to seismically
slipping patches• Stress overshoot during ruptures
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Effect of Overshoot on Rupture Characteristics
Large overshoot (13%)
Small overshoot (1%)
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Approximations to Elastodynamics Values for rupture parameters determined by comparison with fully dynamic rupture models
DYNA3D – Fully dynamic finite element simulation
RSQsim – Fast simulation
Propagation time 14.0 s
Propagation time 14.3 s
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Smooth Initial Stress (w/ block of higher normal stress)
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• Rate-strengthening (a > b) patches– Approximated as always sliding at steady-state– Distributed as
• Deep creeping extensions to major faults• Shallow creep on major faults• Entire creeping sections (e.g. SAF north of Parkfield)
– Possibly with small imbedded stick-slip patches
• More complicated mixed stick-slip and creeping areas (e.g. Hayward Fault)
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Penetration of slip of large events into creeping zone
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Fraction of moment release in creeping section
Aftershocks
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1989 Loma Prieta EarthquakeSimulation
Omori's law R t 1
Omori's law R t 1
Small repeating earthquakes
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Power-law temporal clustering
Decay of aftershocks follows Omori power law t -p with p = 0.77
Foreshocks (not shown) follow an inverse Omori decay with p = 0.92
Dieterich and Richards-Dinger, PAGEOPH, 2010
Stacked rate of seismicity relative to mainshock origin time
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Power-law temporal clustering
Interevent Waiting Time DistributionsCalifornia Catalog 1911 – 2010.5
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Power-law temporal clustering
Space – Time Distributions
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Earthquake cluster along San Andreas Fault
M7.3 43 aftershocks in 18.2days
All-Cal model – SCEC Simulator Comparison Project
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Earthquake cluster along San Andreas Fault
M6.9 Followed by 6 aftershocks in 4.8 minutes
All-Cal model – SCEC Simulator Comparison Project
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Earthquake cluster along San Andreas Fault
M7.2
All-Cal model – SCEC Simulator Comparison Project
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• slip ~2.3 - 4.0 cm
• duration ~10-40 days
• inter-event time - ~10-19 months
• simultaneous slip in different areas
• no Omori clustering
• spontaneous segmentation
Colella et al.,submitted
Colella et al.,submitted
Slow-slip events
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Summary or Conclusions (if appropriate or desired)